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Further observations on the morphology of atrioventricular septal defects
J
THORAC CARDIOVASC SURG
90:611-622, 1985
Further observations on the morphology of atrioventricular septal defects Certain morphologic aspects of atrioventricular septal defects ("endocardial cushion defects," "atrioventricular canal malformations") remain controversial. It is still not clear which precise lesions should not be placed in this category. For example, is an "isolated" cleft of the mitral valveor a perimembranolti inlet ventricularseptal defect to beso described? It is also not fully accepted that the left atrioventricular valve in these lesions bears little resemblance to a morphologically mitral valve. We have investigated these problems by both observation and mensuration. We determined the junctional circumference of the left atrioventricular valveleaflets and the ventricular dimensions in 130 atrioventricular septal defects (95 with common valve orifice and 35 with separate right and left atrioventricular orifices~ in SO hearts with perimembranolti venticular septal defects (20 extending into the inlet septum and 30 with outlet or trabecular extensions~ in seven hearts with isolated cleft of the mitral valve, and in 10 normal hearts. All specimens came from the cardiopathological collection of Children's Hospital of Pittsburgh. The measurements showed conclltiively that the atrioventricular septal defects were all directly comparable irrespec~ve of the detailed morphology of the atrioventricular valve or valves. The group of atrioventricular septal defects was totally discrete as compared with all the other specimens that had normal atrioventricular septation. The left atrioventricular valve in atrioventricular septal defects is basically a three-leaflet valve which differs from the normal mitral valve in terms of its leaflet, its chordal support, and the arrangement of its papillary muscle, Its only similarity with the normal mitral valve is that it resides in the morphologically left ventricle and guards the left atrioventricular junction.
Patricia A. Penkoske, M.D.,* William H. Neches, M.D.,** Robert H. Anderson, M.D.,*** and James R. Zuberbuhler, M.D.** Pittsburgh. Pa.
here have been numerous investigations concerning the morphology and classification of so-called "endocardial cushion defects" or "atrioventricular canal malformations."'" As described recently," it is more accurate from an anatomic standpoint to characterize these From the Division of Cardiology, Children's Hospital of Pittsburgh, Pittsburgh, Pa. During the course of this investigation Dr. Penkoske was a visiting researcher at Children's Hospital of Pittsburgh and Professor Anderson was on sabbatical leave supported by the British Heart Foundation and the Patrick Dick Memorial Fund. Received for publication Dec. 4, 1984. Accepted for publication Dec. 28, 1984. Adress for reprints: J. R. Zuberbuhier, M.D., Division of Cardiology, Children's Hospital of Pittsburgh, 125 DeSoto St., Pittsburgh, Pa. 15213. "Cardiothoracic Surgeon, University of Alberta, Edmonton, Alberta, Canada. ··Professor of Pediatrics, Children's Hospital of Pittsburgh. •••Joseph Levy Professor of Paediatric Cardiac Morphology, Cardiothoracic Institute, Brompton Hospital, London, United Kingdom.
lesions in terms of a deficiency of atrioventricular septation. The term "atrioventricular septal defect" then emphasizes the abnormal morphology of the atrioventricular septal junction, which is common to all these malformations and which is the key to their understanding. First, the aorta is in an anterior unwedged position so that, in presence of ventriculoarterial concordance, there is a long and potentially stenotic left ventricular outflow tract (the "goose-neck abnormality"). Second, there is a disparity in the inflowjoutflow dimensions (normally equal) of the left ventricle. Coupled with this is a deficiency of the midportion of the septum, giving it a characteristically "scooped" appearance. Third, there is a common atrioventricular junction guarded by a unique five-leaflet valve. The left ventricular component of this valve differs from the normal mitral valve in all its parts: anulus, leaflets, and papillary muscles. Finally, and perhaps most importantly, almost always there is the anatomic potential for shunting through the deficiency at the site of the normal atrioventricular septum.
611
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Hearts with Normal AV Septation
Thoracic and Cardiovascular Surgery
aim is to address in a more scientific way the highly contentious issue of the morphology of the left ventricular component of the atrioventricular valve. We will do this by mensuration, comparing the valve in atrioventricular septal defects with the normal mitral valve and the left valve in those hearts sometimes considered as atrioventricular septal defects, namely perimembranous inlet ventricular septal defects and so-called "isolated" cleft of the mitral valve. In this way we will show, as previously described by Rastelli, Kirklin, and Titus' and emphasized by Carpentier,'? that there is no resemblance between the left valve of atrioventricular septal defects and the mitral valve in hearts with normal atrioventricular septation.
Material and methods
Atrioventricular Septal Defects
Fig. 1. Diagram showing the measurements made on the left ventricular aspect to determine the inlet, outlet, and (in the case of the atrioventricular septal defects) the degree of "scooping" of the ventricular septum. A V, Atrioventricular.
However, there are differences in the anatomy among hearts within the overall group which produce marked dissimilarity in clinical presentation. First, the common atrioventricular junction may be guarded by a common valve or by separate right and left valves. Second, according to the relationships of the bridging leaflets of the common valve to the atrial and ventricular septal structures, which themselves may be additionally deficient, the anatomic potential for shunting through the septal defect may be at atrial or ventricular levels. Despite (or perhaps because of) the voluminous literature, there remain aspects of the overall morphology of this group of hearts that are controversial. In this report it is our hope to mitigate some of these disagreements. We have two main aims. The first is to show that the distinction between the variants with common valve orifice or separate right and left orifices is, in anatomic terms, simply one of degree. We will therefore emphasize the marked similarities between them in terms of the morphology of the ventricular mass and atrioventricular valve leaflets while not ignoring their obvious differences. We will also show that other hearts, often considered to be "endocardial cushion defects," have none of the anatomic stigmata of this group. Our second
One hundred eighty seven specimens from the Heart Museum of the Children's Hospital of Pittsburgh were examined. There were 130 having atrioventricular septal defects, 95 with common atrioventricular valve orifices (so-called "complete" variants) and 35 with separate right and left valve orifices (so-called "partial" variants or "ostium primum atrial septal defect"). Specimens of atrioventricular septal defect with either atrial isomerism ("splenic syndromes") or ventriculoarterial discordance ("transposition") were excluded. Seven hearts had a so-called "isolated" cleft of the aortic leaflet of the mitral valve in the absence of an atrioventricular septal defect, although all had other types of atrial and/or ventricular septal defects. Fifty hearts with a perimembranous ventricular septal defect were studied. Twenty of these had the perimembranous deficiency of the ventricular septum confined to the inlet muscular component. In the other 30 it was the outlet and/or the trabecular parts of the muscular septum that were deficient. We also studied 10 hearts having no congenital cardiac lesions ("normals"). In all the specimens we made measurements of the inlet and outlet dimensions of the left ventricle (Fig. I). The outlet was measured from the anterior attachment of the aortic valve to the left ventricular apex and the inlet from the apex to the crux. In those hearts with deficiency of atrioventricular septation, we also measured the degree of "scooping" of the septum and compared this to the outlet dimension. The measurement of the scooped segment was taken from the point of maximum excavation to the apex. In all the hearts we measured the dimensions of the left atrioventricular valve. In those without a deficiency of atrioventricular septation, we compared the length of circumferential annular attachment of the aortic (anterior) leaflet to that of the mural (posterior) leaflet (Fig. 2). In those
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Atrioventricular septal defects
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(Valves viewed from above) Superior
Inferior vs. (1)
M M+S'+I'
Normal mitral valve
or
M
M + S"+ I"
Left valve in AV septal defect
Fig. 2. Diagram showing the measurements made of the (left) mitral valve in hearts with normal atrioventricular septation and (right) the left atrioventricular valve in atrioventricular septal defects.
Fig. 3. The leaflet arrangement in an atrioventricular septal defect with common atrioventicular orifice and minimal bridging of the superior leaflet (so-called Rastelli type A arrangement). The heart is viewed (a) from the right ventricular inlet aspect and (b) from the infundibular aspect. AV, Atrioventricular. PM, Papillary muscle.
with an atrioventricular septal defect we measured the annular circumferential attachment of the.mural leaflet as well as those of the left ventricular components of the superior and inferior bridging leaflets. This was done in two ways. First, we took account only of the attachments of the bridging leaflets to the common anulus. The second method was to include also the portions of the
bridging leaflets that were attached to the crest of the ventricular septum. Other features evaluated were the anatomy of the right and left ventricular papillary muscles and the type of leaflet attachment to them. In the atrioventricular septal defects we also studied the morphology and relationship of the bridging leaflets. The presence of
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Fig. 4. The extreme bridging of the superior leaflet, with concomitant decrease in size of the anterosuperior (ant.sup.) leaflet in an atrioventricular septal defect with common valve orifice (so-called Rastelli type C arrangement). The heart is viewed from the right ventricular inlet aspect.
associated defects and Down's syndrome were tabulated.
Nomenclature of the leaflets A brief review of the nomenclature to be used in describing the leaflets is probably in order (see reference II and Fig. 4). In the normal heart we recognize aortic (anterior) and mural (pos.terior) leaflets in the mitral valve. In the tricuspid valve, there are septal, anterosuperior, and mural (inferior) leaflets. In atrioventricular septal defects, be there a common valve orifice or separate right and left orifices, the valve possesses five leaflets. Two of these leaflets are common to both ventricles; the superior and inferior bridging leaflets. In using this terminology we are following the precedent of the Birmingham group, 12.13 since previously we described them as anterior and posterior. The anterior/ posterior nomenclature is of value to the anatomist, but the superior/inferior appelation is more appealing to the surgeon and correlates much better with angiocardiographic observations. Of the other three leaflets, one is confined to the left ventricle. This is the left mural leaflet. The other two are confined to the right ventricle, the anterosuperior and right mural (inferior) leaflets, respectively.
Results Arrangement of the papillary muscles in atrioventricular septal defects. In the right ventricle. Either two or three papillary muscles were found in the atrioventricular septal defects with a common valve orifice. The anterior papillary
The Journal of Thoracic and Cardiovascular Surgery
muscle, located at the base of the septomarginal trabecula, was invariably present and was usually the largest muscle. Itsupported the commissure between the anterosuperior and the right mural leaflets, and sometimes also the free edge of the anterosuperior leaflet. The inferior muscle was also invariably present, was smaller, and supported the commissure between the right mural and inferior bridging leaflets. There was considerable variation in the position of the medial papillary muscle group or its analogue. In 38 hearts it was found more-or-less in its normal position and supported the commissure between the superior bridging and anterosuperior leaflets. This gave the so-called Rastelli type A arrangement (Fig. 3). In 26 of these hearts there was only minimal bridging of the superior leaflet across the crest of the ventricular septum; in the other hearts the bridging was more marked. In a further 23 hearts there was no muscle at the anticipated site of the medial group. Instead, there was extreme bridging of the superior leaflet, and the commissure between it and the much-reduced anterosuperior leaflet was supported by a large anterior muscle that also supported the commissure between the anterosuperior and right mural leaflets. This is the so-called Rastelli type C lesion (Fig. 4). In between these two extremes, the commissure between the superior bridging and anterosuperior leaflets was supported by a muscle intermediate in position between the medial and anterior muscles. In IS hearts the muscle was part way down the body of the septomarginal trabecula, as in the Rastelli type B variant (Fig. 5). In a further nine hearts, the muscle was directly adjacent to the anterior papillary muscle. We grouped these latter hearts as B/C lesions. Together, the Band B/C hearts made up 27% of the hearts we were able to categorize. In all the atrioventricular septal defects with separate right and left valve orifices, there were three papillary muscles present. The anterior and inferior muscles were all disposed as described earlier. There was variation in the arrangement of the medial muscle. In all but one heart it was in its normal position on the posterior limb of the septomarginal trabecula. There was further variability among these 22 hearts in the arrangement of the superior bridging leaflet. In 20 the leaflet was turned-in as it crossed the septum and was attached in linear fashion to the right ventricular side of the septum. Consequently, there was an apparent deficiency in the "septal leaflet of the tricuspid valve," in reality the tied-down bridging component of the superior leaflet (Fig. 6, a). In some of these, the turned-in edge was perforate, which gave the potential for interventricular shunting (Fig. 6, b) (see below). Overall, the arrange-
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Atrioventricular septal defects
Fig. 5. The intermediate bridging of the superior leaflet, which is tethered by an anomalous papillary (pap.) muscle, in an atrioventricular septal defect with common valve orifice (so-called Rastelli type B arrangement). The heart is viewed (a) from the right ventricular inlet aspect and (b) from the infundibular aspect.
Fig. 6. The arrangement of the superior bridging leaflet in atrioventricular septal defects with separate valve orifices (so-called ostium primum atrial septal defects). The heart in (a) has the entire length of the leaflet turned in and attached in linear fashion to the right ventricular aspect of the septum. It is seen from the inlet aspect. In (b), viewed from the infundibular aspect, the leaflet is turned in, but there are small perforations along its septal attachment which would offer the potential for small interventricular communications. Note that the so-called "cleft" is the space between the left ventricular (LV) components of the bridging leaflets.
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Fig. 7. A more unusual arrangement of the bridging leaflet and connecting tongue in an atrioventricular (AV)septal defect with separate right and left atrioventricular orifices. The leaflet tissue is liberated on the right ventricular aspect to give a separate right septal leaflet. The raphe beneath the leaflet is, in effect, an interventricular membranous septum.
Fig. 8. An unexpected finding in one of our cases of atrioventricular septal defect with separate right and left valve orifices (ostium primum atrial septal defect). There is a connecting tongue between the leaflets so that there are two discrete valve orifices, but the papillary muscle (p.rn.) supporting the superior bridging leaflet is in the position anticipated for a so-called Rastelli type B arrangement. LV, Left ventricular.
ment in these hearts was comparable to the Rastelli type A variant found with common valve orifice (compare Figs. 3 and 6). In two of the hearts with the medial papillary muscle in its usual position, the edge of the right ventricular component of the superior bridging leaflet was not turned-in. Instead, it was liberated from an underlying interventricular membranous septum and attached by chords to the septum. It was then continuous via a liberated leaflet segment derived from the connecting tongue with the inferior bridging leaflet, the whole arrangement producing a continuous "septal" leaflet of the right atrioventricular valve (Fig. 7). In the remaining heart, the arrangement of the superior bridging leaflet was comparable to the Rastelli type B variant. Although there were two separate valve orifices, the commissure between the superior bridging and anterosuperior leaflets was supported by an anomalously positioned papillary muscle arising from the body of the septomarginal trabecula (Fig. 8). Left ventricular papillary muscles. The arrangement of the muscles was the same in all hearts with a
deficiency of atrioventricular septation, whether a common valve or two separate valves were present. This morphology was different from that found in the normal hearts, the hearts with isolated mitral valve clefts, and those with perimebranous ventricular septal defects. In the hearts with normal atrioventricular septation, the muscles were obliquely situated in the posteromedial and anterolateral position (Fig. 9). The posteromedial muscle hugged closely the inlet part of the ventricular septum. In the hearts with atrioventricular septal defects, the muscles were in the same vertical plane and positioned superiorly and inferiorly (Fig. 10). The muscles were usually equal in size and supported the commissures between the bridging leaflets and the left mural leaflet. However, seven hearts with separate valve orifices (20%) had additional malformations. In three, abnormal chordal attachment from the inferior bridging leaflet and inferior papillary muscle produced a dualorifice left valve. In four cases there was a single papillary muscle, giving the so-called parachute deformity. In only three of the hearts with common valve
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Atrioventricular septal defects
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Fig. 9. A short-axis cut across the ventricular mass (viewed from beneath so that the right side is the to the right) in a heart with normal atrioventricular septation, It shows the overlapping of the inlet and outlet components of the left ventricle and the oblique arrangement of the paired papillary muscles of the mitral valve. RV, Right ventricular, Ant., Anterior. Post" Posterior. R, Right. L, Left.
orifice (3.1%) were there abnormalities of the left valve. Two hearts had a parachute arrangement and the other had a dual orifice.
The bridging leaflets in atrioventricular septal defects. The superior bridging leaflet. The detailed anatomy of this leaflet and its connections in the right ventricle have been described earlier in the section devoted to the papillary muscles.
Fig. 10. A short-axis cut (in comparable orientation to Fig. 9) in a heart with deficient atrioventricular septation showing the left half of the common atrioventricular junction as seen from beneath. Note that the outflow tract is no longer wedged between the inlet and the septum, Note also that the inferior papillary muscle is displaced laterally to produce "in-line" rather than oblique muscles. The final effect is to produce a trifoliate left atrioventricular valve (LA VV).
The inferior bridging leaflet. WITH SEPARATE ORIFICE. In all but one case the inferior bridging leaflet was a solitary structure equally committed to both ventricles. The leaflet was firmly attached to the septum and gave no potential for ventricular shunting. In the outstanding case the leaflet was bifid and a small shunt through interchordal spaces would have been possible. WITH COMMON ORIFICE. A bifid leaflet was present in 12 cases (Fig. II, b). The potential for either interchordal (eight) or free (two) shunting was present in 10 of these. With a solitary inferior leaflet (Fig. 11, a) the potential for free (15), interchordal (33), or no shunting (seven) was present.
Relationship of superior and inferior bridging leaflets. WITH SEPARATE ORIFICES. In the majority of cases (16/23), the superior and inferior bridging leaflets together with the connecting tongue were fused to the underlying ventricular septum, so that there was no potential for interventricular shunting. In two cases the
superior bridging leaflet was free. In one of these, the leaflet was fixed to an anomalously located medial papillary muscle located on the right ventricular septum (Fig. 8). In five cases there was the potential for interventricular shunting through interchordal spaces. These spaces were under the superior bridging leaflet alone in two cases (Fig. 4), under both the superior and inferior bridging leaflets in one, under the tongue alone in one, and beneath the superior and inferior bridging leaflets together with the tongue in another. WITH COMMON ORIFICE. The relationship was looked at in two ways. First, we were concerned with the . potential for shunting under the superior bridging leaflet (none, through interchordal spaces, or under a free leaflet) (Table I). If the superior leaflet was firmly fixed to the septum, so was the inferior leaflet (2/2). If there was the potential for interchordal shunting under the superior leaflet, there was similar potential under the inferior leaflet in 75% of the cases. A free superior leaflet was almost equally associated with a potential
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Fig. I I. The two common patterns of the inferior bridging leaflet found in atrioventricular septal defects with common valve orifice. Both are sectioned in a four-chamber plane. There is a common floating leaflet in (a), while in (bj the leaflet is divided by a raphe along the septum, with chords producing septal tethering. RA, Right atrium. RV, Right ventricle. LA, Left atrium. L V, Left ventricle. A V. Atrioventricular.
Table I. Relationship of inferior to superior bridging leaflet
Table II. Rastelli classification and leaflet morphology
No·~1 No,
No
VSD
I
lnterchordai shunt
I
No VSD
Intcrchordal 2 24 44
2 3 4
Free
18 23
~
7
3 20
Superior bridging leaflet Free
Superior No VSD Interehordal shunt Free leaflet
B-C
3 17
l.egend: YSD. Ycntricular septal defect.
free or interchordal communication under the inferior leaflet. The second way was to divide the group into the Rastelli subtypes and look at the anatomic potential for shunting (Table II). A free communication beneath the superior bridging leaflet was much more common with the types B, B/C, and C. In the types A and B, it was more common to have interchordal rather than free communication under the inferior leaflet. In the B/C and C varieties, it was equally or more likely to have the anatomic potential for free shunting, In only two hearts of the 70 cases that we were able to categorize was the potential for shunting greater under the inferior than the superior leaflet.
No VSD
Interchordal Free
.
2
2
24 44
20 7
I 10
Inferior bridging leaflet 9 5 3 41 20
21 3
7 1
1
4
3
9 13
Legend: YSD. Ycntricular septal defect.
Comparison of atrioventricular septal defects with other hearts. Ratio of the inlet/outlet dimension of the left ventricle. The value of the inlet/outlet dimensions was significantly less in hearts with atrioventricular septal defects than in those with perimembranous ventricular septal defects, isolated mitral "clefts," or structurally normal hearts. There was no significant difference between the values for the groups with separate versus common orifices or between the Rastelli subtypes (Table III). Ratio of the scooped portion/outlet dimension of the left ventricle. There was no significant difference
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Atrioventricular septal defects
Table ID. Inlet/outlet (I/O) left ventricular dimensions Normal hearts Cleft mitral valve Ventricular septal defect Perimemb. inlet Perimemb. outlet/trab, Atrioventricular septal defects* Separate orifices Common orifice A B B-C C
No.
I/O ± SD
10 7
0.99 ± 0.01 0.98 ± 0.03
20 30
0.98 ± 0.02 0.98 ± 0.02
35 85 38 15 9 23
0.76 0.74 0.73 0.75 0.76 0.75
± ± ± ± ±
±
0.07 0.08 0.07 0.09 0.06 0.09
Legend:SD, Standard deviation. "The difference between the values for atrioventricular septal defects and the other hearts is statistically significant (p < 0.001) in each comparison.
between the groups with separate or common orifices or between the Rastelli subtypes (Table IV). Morphology of the left atrioventricular valve. In the 10 normal hearts, the circumferential attachment of the mural leaflet made up 64% of the entire annular circumference of the mitral valve. The measurements for isolated "clefts" and for all hearts with perimembranous ventricular septal defects showed no significant difference to the normal (Table V). In contrast, the attachment of the mural leaflet was significantly smaller for all atrioventricular septal defects (p < 0.001), whichever of the two methods of measurement was used (see Fig. 2). There was no significant difference among the different types of atrioventricular septal defect. Additional malformations in atrioventricular septal defects. Presence of associated defects. Associated defects were present in both separate and common orifice cases (Table VI). Abnormal outflow tract malformations (tetralogy of Fallot and double-outlet right ventricle), total anomalous pulmonary venous connection, and pulmonary atresia were all more frequent in association with common orifice. Left atrioventricular valve abnormalities and hypoplastic left ventricle were more frequent in the group with separate orifices. Coarctation was associated with both groups. Except for the more frequent association of right ventricular outflow tract abnormalities and free-floating leaflets and, in this series, hypoplastic left ventricle with minimal bridging of the superior leaflet, there was no pattern of specific anomalies associated with the Rastelli subtypes. Presence of Down's syndrome. Of the 35 specimens with a separate atrioventricular orifice, only four (11 %) were obtained from patients with Down's syndrome. None of these hearts had any associated defects.
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Table IV. Ratio of scooped portion ventricular
septum/outlet dimension of left ventricle (8/0) S/O
No. Separate orifice Common orifice A B B-C C
0.67 0.59 0.57 0.63 0.59 0.58
35 85 38 15 9 23
± ± ± ± ± ±
0.07* 0.08* 0.08 0.10 0.05 0.08
"The difference is not statistically significant.
Table V. Left atrioventricular valve-eircumferential
attachment of mural leaflet Circumference Normal hearts Isolated cleft Ventricular septal defect Perimemb. inlet 20 30 Preimemb. outler/trab. Atrioventricular septal defects* Separate orifices 35 Common orifice 85 A 38 B 15 B-C 9 C 23
0.64 ± 0.04 0.60 ± 0.03 0.61 ± 0.05 0.62 ± 0.06 Method 1 0.30 ± 0.08 0.31 ± 0.07 0.28 ± 0.07 0.33 ± 0.07 0.34 ± 0.06 0.34 ± 0.07
Method 2 0.17 ± 0.06 0.18 ± 0.05 0.15 ± 0.05 0.20 ± 0.05 0.21 ± 0.05 0.19 ± 0.05
"The difference between the values for atrioventricular septal defects and the other hearts are statistically significant (p < 0.001) whichever method of measurement is considered.
Down's syndrome was more common in the group with a common atrioventricular orifice, 39 of 95 specimens (41%). Again, there was a paucity of associated defects (Table VII). There was no propensity for any of the Rastelli subtypes. Discussion Our further study of hearts with deficient atrioventricular septation has endorsed the measurements performed and the conclusions drawn by Piccoli and associates.?" Indeed, they go further and provide hard scientific evidence to support the contention of Becker and Anderson" that, if the valve leaflets are removed, there is no way of distinguishing the variants of this group from one another. However, while our measurements show conclusively that all lesions with the stigmata of atrioventricular septal defects have a comparable ventricular mass and atrioventricular junction, they also show that other hearts often grouped with these malformations do not share these unifying features. Thus, it is often suggested that hearts with a perimembranous deficiency of the muscular inlet septum, and others with an isolated "cleft" in the anterior (aortic) leaflet of the mitral valve, should be considered as "formes fruste" or
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Table VI. Associated anomalies Common orifice In = 95)
Separate orifices In = 35)
I
No.
10 10 0 3
Hypoplastic left ventricle Coarctation TOF/DORV Double-orifice left A V valve Parachute left AV valve Ebstein's right AV valve Total anomalous pulmonary VC Pulmonary atresia Duct Hypoplastic right ventricle Down's syndrome
29 29 9 II
4 I
3
0 0 4
II
4
II
I.
No.
%
%
10
II
21 19 I
22 20
2 2
2 2
2 5 6 I 39
2 3
I
6 I 41
Rastelli type Anomaly Hypoplastic left ventricle Coarctation TOF/DORV Left AV valve abnormality Pulmonary atresia Right AV valve abnormality TAPVC Hypoplastic right ventricle Duct Down's syndrome
No.
A
10
6
21 19
10 3
3 5
I I
2 2
I
B I I 4 I
I
BIC
I
I 4
3 13
2 8 6 I
2
2
I
I I I
I
6 39
C
8
5
I
Unclassified* I I 2
2
I
8
5
Legend: TOF, Tetralogy of Fallot, DORV, Double-outlet right ventricle. AV, Atrioventricular. VC, Venous connection. 'Usually a postoperative specimen in which this specific feature was unclear.
"incompletely expressed" examples of atrioventricular septal defects (atrioventricular canal malformations, endocardial cushion defects}.14, 15 This is not the case. Hearts in neither of these categories have anything in common with atrioventricular septal defects in terms of their overall anatomy. This is particularly significant in the case of an isolated "cleft" of the mitral valve.15 We will discuss in depth the matter of the left valve in atrioventricular septal defects. Suffice it at this stage to indicate that, very rarely, hearts can exist with all the stigmata of an atrioventricular septal defect, including a trifoliate left valve, but with intact septal structures." If hearts are to be defined as "incompletely expressed" examples of this group, it is the latter anomalies that should be thus considered. Our study has therefore clarified for us with hard measurements the precise nature of what is and what is not an atrioventricular septal defect. It has also enabled us better to appreciate how those lesions in this group with, on the one hand, common orifice and, on the other hand, separate right and left atrioventricular orifices are characterized more by their similarities than by their differences. It is the similarity among the hearts that
defeats attempts to characterize them in terms of "completeness' or "partialness." These subdivisionshave been related more to concepts of embryology than to observations of anatomy. The measurements we have done show that the morphology of the so-called "complete" variant differs from the so-called "partial" variant only in the absence of a connecting tongue of valve tissue between the facing surfaces of the two bridging leaflets. Attempts to classify completeness according to the potential for shunting between the cardiac chambers necessitates the provision of various "intermediate" or "transitional" categories. I, 2, 17 The problem with all these attempts at "pigeon-holing" is that the major variables, namely the state of the atrioventricular orifice and the anatomic potential for shunting through the atrioventricular septal defect, are not mutally dependent. Thus, with a common orifice the anatomic potential for shunting can be confined to the atrial level when the bridging leaflets are firmly adherent to the septum although not joined by a connecting tongue. Similarly, hearts with separate right and left orifices can exist with free-floating leaflets so that there is anatomic potential for considerable shunting at the ventricular level.All this
Volume 90 Number 4 October, 1985
information cannot be conveyed in a single term. Instead, it is preferable to describe separately the state of the atrioventricular junction (common orifice or separate orifices) and the anatomic potential for shunting between the cardiac chambers. The other areas in which attempts have been made to pigeon-hole the anatomy is in the morphology of the bridging leaflets. In this respect, the seminal study of Rastelli, Kirklin, and Titus' represented a major step forward in our knowledge. As stated by Piccoli and colleagues," subsequent studies endorsed the observations of this group' but questioned their interpretation. Our present study confirms this opinion. Furthermore, examination of our hearts shows that the spectrum they described can be expanded to include examples with separate valve orifices. When the Rastelli classification' is interpreted in terms of degree of bridging of the superior leaflet rather than division of a common leaflet, then it can easily and logically be expanded to incorporate those hearts with separate valve orifices (ostium primum atrial septal defect). Rastelli, Kirklin, and Titus' themselves in a footnote (reference 33, p. 308) pointed to the analogy between their type A lesion and the arrangement of the normal tricuspid valve. McGoon, Puga, and Danielson 14 then showed that in most "partial" defects the anterior component of the septal leaflet of the tricuspid valve was deficient. Our study endorses their observation. However, deficiency of the leaflet is caused by the superior bridging leaflet being turned-in to be attached in linear fashion to the right ventricular surface of the septum. Our specimens show the intermediate forms of this spectrum, in which the right ventricular component of the superior leaflet stands free in the presence of separate orifices. Furthermore, in a single specimen we observed increased bridging of the superior leaflet comparable to the Rastelli type B variant but still with separate right and left valve orifices. The only logical interpretation of these findings is that presaged by Studer and co-workers," namely that the spectrum of lesions incorporated within the Rastelli classification be expanded to include cases with separate valve orifices (partial defects or ostium primum atrial septal defect). Having said that, we must then ask if this categorization will be of surgical significance. McGoon, Puga, and Danielson 14 are convinced of its value. Others are less so. I I. 18 There is no doubt concerning its anatomic validity. There are, however, significant differences in the observations obtained at autopsy-" and those at operation. Surprisingly few type B variants are observed by the surgeon. Yet these lesions made up 15% of the original series' and 18% of our hearts. A further 11% of our cases were intermediate between
Atrioventricular septal defects
621
Table VB. Down's syndrome and associated anomalies Down's syndrome Non-Dawn's Defect Hypoplastic left ventricle Coarctation TOF/DORV Double-orifice left A V valve Parachute left A V valve Ebstein's right A V valve Total anomalous pulmonary VC Pulmonary atresia Duct Hypoplastic right ventricle
(n = 39)
(n = 56)
I
9
5
16
2
17
o
2 2 2 5 4 I
o
o o o 2 2
I
For legend see Table VI.
types B anc C. The reason for this was pointed out by Rastelli, Kirklin, and Titus. 3 The anomalous papillary muscle supporting the commissure between the superior bridging and the anterosuperior leaflet is best seen from the infundibular aspect, a view unfortunately denied in most cases to the surgeon. Thus, the important subtlety of the Rastelli classification is rarely of full value in the operating room. The other potential disadvantage of the classification is that it took no cognizance of the inferior bridging leaflet. Rastelli, Kirklin, and Titus' and subsequent investigators have suggested that there is no relationship between the state of the inferior leaflet as compared with the superior one. Our findings would suggest this to be an overstatement. In terms of tethering of the leaflet, the arrangement was the same for both leaflets in a significant number of hearts. This relationship, however, was insufficiently constant to be predictive. Each case must therefore be treated on its own merits and examined carefully to determine the morphology and attachments of both bridging leaflets. We can endorse the statement of Ebert and Goor" that, almost without exception, the greatest potential for shunting is beneath the superior bridging leaflet. The adjudication of the surgical value of these observations requires further studies in the mold of that of Studer and associates," which analyzes the whole spectrum of atrioventricular septal defects. The outstanding question concerning atrioventricular septal defects remains the nature of the left atrioventricular valve. The anatomic nature of this valve has been obscured by two features. First, the categorization of the lesions has been conducted on embryologic rather than anatomic premises. Second, there has been disagreement concerning the role in surgical repair of closure of the so-called "cleft." Both of these matters are extraneous to the anatomic issues. Our present study has shown
. The Journal of
6 2 2 Penkoske et al.
unequivocally that the left valve in atrioventricular septal defects bears resemblance neither to the normal mitral valve nor to the mitral valve with a perimembranous inlet, ventricular septal defect, or with an isolated "cleft." This observation is certainly not original. The potential dangers in closing the so-called "cleft" were discussed by both Frater" and Van Mierop and Alley." At more-or-less the same time, Rastelli, Kirklin, and Titus' commented that "it is concluded that the term is inappropriate." Yet the use of the term persisted, as did the concept of a naturally occurring breach between the components of the anterior leaflet of the mitral valve. It is Carpentier" who deserves the credit for emphasizing that the left valve differs not only in terms of the leaflets but also in terms of papillary muscle disposition, but even he continued to call it a mitral valve. Why should we call it a mitral valve when it has none of the features associated with that structure other than residing within the morphologically left ventricle? The merits of closing or not closing the functional commissure ("cleft") between the left ventricular components of the bridging leaflets remain to be established in a scientific manner. We submit that this will be accomplished only when it is fully appreciated that the left valve in atrioventricular septal defects is a trifoliate structure with scant resemblance to the normal mitral valve. The significance of this single fact is clearly demonstrated in the recent and excellent study of Rizzoli and his colleagues.22
2
3
4
5 6
7
8
REFERENCES Wakai CS, Edwards JE: Developmental and pathologic considerations in persistent common atrioventricular canal. Mayo Clin Proc 31:487-500, 1956 Wakai CS, Edward JE: Pathologic study of persistent common atrioventricular canal. Am Heart J 56:779-794, 1958 Rastelli GC, Kirklin JW, Titus JL: Anatomic observations on complete form of persistent common atrioventricular canal with special reference to atrioventricular valves. Mayo Clin Proc 41:296-308, 1966 Goor D, Lillehei CW, Edwards JE: Further observations on the pathology of the atrioventricular canal malformation. Arch Surg 97:954-962, 1968 Bharati S, Lev M: The spectrum of common atrioventricular orifice (canal). Am Heart J 86:553-561, 1973 Ugarte M, de Salamanca FE, Quero M: Endocardial cushion defects. an anatomical study of 54 specimens. Br Heart J 38:674-682, 1976 Piccoli GP, Gerlis LM, Wilkinson JL, Lozsadi K, Macartney FJ, Anderson RH: Morphology and classification of atrioventricular defects. Br Heart J 42:621-632, 1979 Piccoli GP, Wilkinson JL, Macartney FJ, Gerlis LM,
Thoracic and Cardiovascular Surgery
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10
11
12
13
14
15
16
17
18
19
20
21
22
Anderson RH: Morphology and classification of complete atrioventricular defects. Br Heart J 42:633-639, 1979 Becker AE, Anderson RH: Atrioventricular septal defects. What's in a name? J THORAC CARDIOVASC SURG 83:461469, 1982 Carpentier A: Surgical anatomy and management of the mitral component of atrioventricular canal defects, Paediatric Cardiology 1977, RH Anderson, EA Shinebourne, eds., Edinburgh, 1978, Churchill Livingstone, pp 477486. Anderson RH, Zuberbuhler JR, Penkoske PA, Neches WH: Of clefts, commissures, and things. J THORAC CARDIOVASC SURG 90:605-610, 1985 Berger TJ, Kirklin JW, Blackstone EH, Pacifico AD, Kouchoukos NT: Primary repair of complete atrioventricular canal in patients less than 2 years old. Am J Cardiol 41:906-913, 1978 Studer M, Blackstone EH, Kirklin JW, Pacifico AD, Soto B, Chung GKT, Kirklin JK, Bargeron LM: Determinants of early and late results of repair of atrioventricular septal (canal) defects. J THORAC CARDIOVASC SURG 84:523-542, 1982 McGoon DC, Puga FJ, Danielson GK: Atrioventricular canal, Gibbon's Surgery of the Heart, DC Sabiston, FC Spencer, eds., Philadelphia, 1983, W. B. Saunders Company, pp 1051-1066 Di Segni E, Edwards JE: Cleft anterior leaflet of the mitral valve with intact septa. A study of 20 cases. Am J Cardiol 51:919-926, 1983 Silverman NH, Ho SY, Anderson RH, Smith A, Wilkinson JL: Atrioventricular septal defect with intact atrial and ventricular septal structures. Int J Cardiol 5:567-572, 1984 Bharati S, Lev M, McAllister HA, Kirklin JW: Surgical anatomy of the atrioventricular valve in the intermediate type of common atrioventricular orifice. J THORAC CARDIOVASC SURG 79:884-889, 1980 Norwood WI, Castaneda AR: Atrioventricular canal defects. Partial, intermediate and complete, Thoracic and Cardiovascular Surgery, WWL Glenn, ed., Norwalk, Conn., 1983, Appleton-Century-Crofts, pp 757-769 Ebert PA, Goor DA: Complete atrioventricular canal malformations. Further clarification of the anatomy of the common leaflet and its relationship to the VSD in surgical correction. Ann Thorac Surg 25:134-143, 1978 Frater R WM: Persistent common atrioventricular canal. Anatomy and function in relation to surgical repair. Circulation 32: 120-129, 1965 Van Mierop LHS, Alley RD: The management of the cleft mitral valve in endocardial cushion defects. Ann Thorac Surg 2:416-423, 1966 Rizzoli G, Mazzucco A, Brumana T, Valfre C, Rubino M, Rocco F, Daliento L, Frescura C, Gallucci V: Operative risk of correction of atrioventricular septal defects. Br Heart J 52:258-265, 1984
THORAC CARDIOVASC SURG
90:611-622, 1985
Further observations on the morphology of atrioventricular septal defects Certain morphologic aspects of atrioventricular septal defects ("endocardial cushion defects," "atrioventricular canal malformations") remain controversial. It is still not clear which precise lesions should not be placed in this category. For example, is an "isolated" cleft of the mitral valveor a perimembranolti inlet ventricularseptal defect to beso described? It is also not fully accepted that the left atrioventricular valve in these lesions bears little resemblance to a morphologically mitral valve. We have investigated these problems by both observation and mensuration. We determined the junctional circumference of the left atrioventricular valveleaflets and the ventricular dimensions in 130 atrioventricular septal defects (95 with common valve orifice and 35 with separate right and left atrioventricular orifices~ in SO hearts with perimembranolti venticular septal defects (20 extending into the inlet septum and 30 with outlet or trabecular extensions~ in seven hearts with isolated cleft of the mitral valve, and in 10 normal hearts. All specimens came from the cardiopathological collection of Children's Hospital of Pittsburgh. The measurements showed conclltiively that the atrioventricular septal defects were all directly comparable irrespec~ve of the detailed morphology of the atrioventricular valve or valves. The group of atrioventricular septal defects was totally discrete as compared with all the other specimens that had normal atrioventricular septation. The left atrioventricular valve in atrioventricular septal defects is basically a three-leaflet valve which differs from the normal mitral valve in terms of its leaflet, its chordal support, and the arrangement of its papillary muscle, Its only similarity with the normal mitral valve is that it resides in the morphologically left ventricle and guards the left atrioventricular junction.
Patricia A. Penkoske, M.D.,* William H. Neches, M.D.,** Robert H. Anderson, M.D.,*** and James R. Zuberbuhler, M.D.** Pittsburgh. Pa.
here have been numerous investigations concerning the morphology and classification of so-called "endocardial cushion defects" or "atrioventricular canal malformations."'" As described recently," it is more accurate from an anatomic standpoint to characterize these From the Division of Cardiology, Children's Hospital of Pittsburgh, Pittsburgh, Pa. During the course of this investigation Dr. Penkoske was a visiting researcher at Children's Hospital of Pittsburgh and Professor Anderson was on sabbatical leave supported by the British Heart Foundation and the Patrick Dick Memorial Fund. Received for publication Dec. 4, 1984. Accepted for publication Dec. 28, 1984. Adress for reprints: J. R. Zuberbuhier, M.D., Division of Cardiology, Children's Hospital of Pittsburgh, 125 DeSoto St., Pittsburgh, Pa. 15213. "Cardiothoracic Surgeon, University of Alberta, Edmonton, Alberta, Canada. ··Professor of Pediatrics, Children's Hospital of Pittsburgh. •••Joseph Levy Professor of Paediatric Cardiac Morphology, Cardiothoracic Institute, Brompton Hospital, London, United Kingdom.
lesions in terms of a deficiency of atrioventricular septation. The term "atrioventricular septal defect" then emphasizes the abnormal morphology of the atrioventricular septal junction, which is common to all these malformations and which is the key to their understanding. First, the aorta is in an anterior unwedged position so that, in presence of ventriculoarterial concordance, there is a long and potentially stenotic left ventricular outflow tract (the "goose-neck abnormality"). Second, there is a disparity in the inflowjoutflow dimensions (normally equal) of the left ventricle. Coupled with this is a deficiency of the midportion of the septum, giving it a characteristically "scooped" appearance. Third, there is a common atrioventricular junction guarded by a unique five-leaflet valve. The left ventricular component of this valve differs from the normal mitral valve in all its parts: anulus, leaflets, and papillary muscles. Finally, and perhaps most importantly, almost always there is the anatomic potential for shunting through the deficiency at the site of the normal atrioventricular septum.
611
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Hearts with Normal AV Septation
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aim is to address in a more scientific way the highly contentious issue of the morphology of the left ventricular component of the atrioventricular valve. We will do this by mensuration, comparing the valve in atrioventricular septal defects with the normal mitral valve and the left valve in those hearts sometimes considered as atrioventricular septal defects, namely perimembranous inlet ventricular septal defects and so-called "isolated" cleft of the mitral valve. In this way we will show, as previously described by Rastelli, Kirklin, and Titus' and emphasized by Carpentier,'? that there is no resemblance between the left valve of atrioventricular septal defects and the mitral valve in hearts with normal atrioventricular septation.
Material and methods
Atrioventricular Septal Defects
Fig. 1. Diagram showing the measurements made on the left ventricular aspect to determine the inlet, outlet, and (in the case of the atrioventricular septal defects) the degree of "scooping" of the ventricular septum. A V, Atrioventricular.
However, there are differences in the anatomy among hearts within the overall group which produce marked dissimilarity in clinical presentation. First, the common atrioventricular junction may be guarded by a common valve or by separate right and left valves. Second, according to the relationships of the bridging leaflets of the common valve to the atrial and ventricular septal structures, which themselves may be additionally deficient, the anatomic potential for shunting through the septal defect may be at atrial or ventricular levels. Despite (or perhaps because of) the voluminous literature, there remain aspects of the overall morphology of this group of hearts that are controversial. In this report it is our hope to mitigate some of these disagreements. We have two main aims. The first is to show that the distinction between the variants with common valve orifice or separate right and left orifices is, in anatomic terms, simply one of degree. We will therefore emphasize the marked similarities between them in terms of the morphology of the ventricular mass and atrioventricular valve leaflets while not ignoring their obvious differences. We will also show that other hearts, often considered to be "endocardial cushion defects," have none of the anatomic stigmata of this group. Our second
One hundred eighty seven specimens from the Heart Museum of the Children's Hospital of Pittsburgh were examined. There were 130 having atrioventricular septal defects, 95 with common atrioventricular valve orifices (so-called "complete" variants) and 35 with separate right and left valve orifices (so-called "partial" variants or "ostium primum atrial septal defect"). Specimens of atrioventricular septal defect with either atrial isomerism ("splenic syndromes") or ventriculoarterial discordance ("transposition") were excluded. Seven hearts had a so-called "isolated" cleft of the aortic leaflet of the mitral valve in the absence of an atrioventricular septal defect, although all had other types of atrial and/or ventricular septal defects. Fifty hearts with a perimembranous ventricular septal defect were studied. Twenty of these had the perimembranous deficiency of the ventricular septum confined to the inlet muscular component. In the other 30 it was the outlet and/or the trabecular parts of the muscular septum that were deficient. We also studied 10 hearts having no congenital cardiac lesions ("normals"). In all the specimens we made measurements of the inlet and outlet dimensions of the left ventricle (Fig. I). The outlet was measured from the anterior attachment of the aortic valve to the left ventricular apex and the inlet from the apex to the crux. In those hearts with deficiency of atrioventricular septation, we also measured the degree of "scooping" of the septum and compared this to the outlet dimension. The measurement of the scooped segment was taken from the point of maximum excavation to the apex. In all the hearts we measured the dimensions of the left atrioventricular valve. In those without a deficiency of atrioventricular septation, we compared the length of circumferential annular attachment of the aortic (anterior) leaflet to that of the mural (posterior) leaflet (Fig. 2). In those
Volume 90 Number 4 October, 1985
Atrioventricular septal defects
6 13
(Valves viewed from above) Superior
Inferior vs. (1)
M M+S'+I'
Normal mitral valve
or
M
M + S"+ I"
Left valve in AV septal defect
Fig. 2. Diagram showing the measurements made of the (left) mitral valve in hearts with normal atrioventricular septation and (right) the left atrioventricular valve in atrioventricular septal defects.
Fig. 3. The leaflet arrangement in an atrioventricular septal defect with common atrioventicular orifice and minimal bridging of the superior leaflet (so-called Rastelli type A arrangement). The heart is viewed (a) from the right ventricular inlet aspect and (b) from the infundibular aspect. AV, Atrioventricular. PM, Papillary muscle.
with an atrioventricular septal defect we measured the annular circumferential attachment of the.mural leaflet as well as those of the left ventricular components of the superior and inferior bridging leaflets. This was done in two ways. First, we took account only of the attachments of the bridging leaflets to the common anulus. The second method was to include also the portions of the
bridging leaflets that were attached to the crest of the ventricular septum. Other features evaluated were the anatomy of the right and left ventricular papillary muscles and the type of leaflet attachment to them. In the atrioventricular septal defects we also studied the morphology and relationship of the bridging leaflets. The presence of
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Penkoske et al.
Fig. 4. The extreme bridging of the superior leaflet, with concomitant decrease in size of the anterosuperior (ant.sup.) leaflet in an atrioventricular septal defect with common valve orifice (so-called Rastelli type C arrangement). The heart is viewed from the right ventricular inlet aspect.
associated defects and Down's syndrome were tabulated.
Nomenclature of the leaflets A brief review of the nomenclature to be used in describing the leaflets is probably in order (see reference II and Fig. 4). In the normal heart we recognize aortic (anterior) and mural (pos.terior) leaflets in the mitral valve. In the tricuspid valve, there are septal, anterosuperior, and mural (inferior) leaflets. In atrioventricular septal defects, be there a common valve orifice or separate right and left orifices, the valve possesses five leaflets. Two of these leaflets are common to both ventricles; the superior and inferior bridging leaflets. In using this terminology we are following the precedent of the Birmingham group, 12.13 since previously we described them as anterior and posterior. The anterior/ posterior nomenclature is of value to the anatomist, but the superior/inferior appelation is more appealing to the surgeon and correlates much better with angiocardiographic observations. Of the other three leaflets, one is confined to the left ventricle. This is the left mural leaflet. The other two are confined to the right ventricle, the anterosuperior and right mural (inferior) leaflets, respectively.
Results Arrangement of the papillary muscles in atrioventricular septal defects. In the right ventricle. Either two or three papillary muscles were found in the atrioventricular septal defects with a common valve orifice. The anterior papillary
The Journal of Thoracic and Cardiovascular Surgery
muscle, located at the base of the septomarginal trabecula, was invariably present and was usually the largest muscle. Itsupported the commissure between the anterosuperior and the right mural leaflets, and sometimes also the free edge of the anterosuperior leaflet. The inferior muscle was also invariably present, was smaller, and supported the commissure between the right mural and inferior bridging leaflets. There was considerable variation in the position of the medial papillary muscle group or its analogue. In 38 hearts it was found more-or-less in its normal position and supported the commissure between the superior bridging and anterosuperior leaflets. This gave the so-called Rastelli type A arrangement (Fig. 3). In 26 of these hearts there was only minimal bridging of the superior leaflet across the crest of the ventricular septum; in the other hearts the bridging was more marked. In a further 23 hearts there was no muscle at the anticipated site of the medial group. Instead, there was extreme bridging of the superior leaflet, and the commissure between it and the much-reduced anterosuperior leaflet was supported by a large anterior muscle that also supported the commissure between the anterosuperior and right mural leaflets. This is the so-called Rastelli type C lesion (Fig. 4). In between these two extremes, the commissure between the superior bridging and anterosuperior leaflets was supported by a muscle intermediate in position between the medial and anterior muscles. In IS hearts the muscle was part way down the body of the septomarginal trabecula, as in the Rastelli type B variant (Fig. 5). In a further nine hearts, the muscle was directly adjacent to the anterior papillary muscle. We grouped these latter hearts as B/C lesions. Together, the Band B/C hearts made up 27% of the hearts we were able to categorize. In all the atrioventricular septal defects with separate right and left valve orifices, there were three papillary muscles present. The anterior and inferior muscles were all disposed as described earlier. There was variation in the arrangement of the medial muscle. In all but one heart it was in its normal position on the posterior limb of the septomarginal trabecula. There was further variability among these 22 hearts in the arrangement of the superior bridging leaflet. In 20 the leaflet was turned-in as it crossed the septum and was attached in linear fashion to the right ventricular side of the septum. Consequently, there was an apparent deficiency in the "septal leaflet of the tricuspid valve," in reality the tied-down bridging component of the superior leaflet (Fig. 6, a). In some of these, the turned-in edge was perforate, which gave the potential for interventricular shunting (Fig. 6, b) (see below). Overall, the arrange-
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Atrioventricular septal defects
Fig. 5. The intermediate bridging of the superior leaflet, which is tethered by an anomalous papillary (pap.) muscle, in an atrioventricular septal defect with common valve orifice (so-called Rastelli type B arrangement). The heart is viewed (a) from the right ventricular inlet aspect and (b) from the infundibular aspect.
Fig. 6. The arrangement of the superior bridging leaflet in atrioventricular septal defects with separate valve orifices (so-called ostium primum atrial septal defects). The heart in (a) has the entire length of the leaflet turned in and attached in linear fashion to the right ventricular aspect of the septum. It is seen from the inlet aspect. In (b), viewed from the infundibular aspect, the leaflet is turned in, but there are small perforations along its septal attachment which would offer the potential for small interventricular communications. Note that the so-called "cleft" is the space between the left ventricular (LV) components of the bridging leaflets.
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Fig. 7. A more unusual arrangement of the bridging leaflet and connecting tongue in an atrioventricular (AV)septal defect with separate right and left atrioventricular orifices. The leaflet tissue is liberated on the right ventricular aspect to give a separate right septal leaflet. The raphe beneath the leaflet is, in effect, an interventricular membranous septum.
Fig. 8. An unexpected finding in one of our cases of atrioventricular septal defect with separate right and left valve orifices (ostium primum atrial septal defect). There is a connecting tongue between the leaflets so that there are two discrete valve orifices, but the papillary muscle (p.rn.) supporting the superior bridging leaflet is in the position anticipated for a so-called Rastelli type B arrangement. LV, Left ventricular.
ment in these hearts was comparable to the Rastelli type A variant found with common valve orifice (compare Figs. 3 and 6). In two of the hearts with the medial papillary muscle in its usual position, the edge of the right ventricular component of the superior bridging leaflet was not turned-in. Instead, it was liberated from an underlying interventricular membranous septum and attached by chords to the septum. It was then continuous via a liberated leaflet segment derived from the connecting tongue with the inferior bridging leaflet, the whole arrangement producing a continuous "septal" leaflet of the right atrioventricular valve (Fig. 7). In the remaining heart, the arrangement of the superior bridging leaflet was comparable to the Rastelli type B variant. Although there were two separate valve orifices, the commissure between the superior bridging and anterosuperior leaflets was supported by an anomalously positioned papillary muscle arising from the body of the septomarginal trabecula (Fig. 8). Left ventricular papillary muscles. The arrangement of the muscles was the same in all hearts with a
deficiency of atrioventricular septation, whether a common valve or two separate valves were present. This morphology was different from that found in the normal hearts, the hearts with isolated mitral valve clefts, and those with perimebranous ventricular septal defects. In the hearts with normal atrioventricular septation, the muscles were obliquely situated in the posteromedial and anterolateral position (Fig. 9). The posteromedial muscle hugged closely the inlet part of the ventricular septum. In the hearts with atrioventricular septal defects, the muscles were in the same vertical plane and positioned superiorly and inferiorly (Fig. 10). The muscles were usually equal in size and supported the commissures between the bridging leaflets and the left mural leaflet. However, seven hearts with separate valve orifices (20%) had additional malformations. In three, abnormal chordal attachment from the inferior bridging leaflet and inferior papillary muscle produced a dualorifice left valve. In four cases there was a single papillary muscle, giving the so-called parachute deformity. In only three of the hearts with common valve
Volume 90 Number 4 October, 1985
Atrioventricular septal defects
6 17
Fig. 9. A short-axis cut across the ventricular mass (viewed from beneath so that the right side is the to the right) in a heart with normal atrioventricular septation, It shows the overlapping of the inlet and outlet components of the left ventricle and the oblique arrangement of the paired papillary muscles of the mitral valve. RV, Right ventricular, Ant., Anterior. Post" Posterior. R, Right. L, Left.
orifice (3.1%) were there abnormalities of the left valve. Two hearts had a parachute arrangement and the other had a dual orifice.
The bridging leaflets in atrioventricular septal defects. The superior bridging leaflet. The detailed anatomy of this leaflet and its connections in the right ventricle have been described earlier in the section devoted to the papillary muscles.
Fig. 10. A short-axis cut (in comparable orientation to Fig. 9) in a heart with deficient atrioventricular septation showing the left half of the common atrioventricular junction as seen from beneath. Note that the outflow tract is no longer wedged between the inlet and the septum, Note also that the inferior papillary muscle is displaced laterally to produce "in-line" rather than oblique muscles. The final effect is to produce a trifoliate left atrioventricular valve (LA VV).
The inferior bridging leaflet. WITH SEPARATE ORIFICE. In all but one case the inferior bridging leaflet was a solitary structure equally committed to both ventricles. The leaflet was firmly attached to the septum and gave no potential for ventricular shunting. In the outstanding case the leaflet was bifid and a small shunt through interchordal spaces would have been possible. WITH COMMON ORIFICE. A bifid leaflet was present in 12 cases (Fig. II, b). The potential for either interchordal (eight) or free (two) shunting was present in 10 of these. With a solitary inferior leaflet (Fig. 11, a) the potential for free (15), interchordal (33), or no shunting (seven) was present.
Relationship of superior and inferior bridging leaflets. WITH SEPARATE ORIFICES. In the majority of cases (16/23), the superior and inferior bridging leaflets together with the connecting tongue were fused to the underlying ventricular septum, so that there was no potential for interventricular shunting. In two cases the
superior bridging leaflet was free. In one of these, the leaflet was fixed to an anomalously located medial papillary muscle located on the right ventricular septum (Fig. 8). In five cases there was the potential for interventricular shunting through interchordal spaces. These spaces were under the superior bridging leaflet alone in two cases (Fig. 4), under both the superior and inferior bridging leaflets in one, under the tongue alone in one, and beneath the superior and inferior bridging leaflets together with the tongue in another. WITH COMMON ORIFICE. The relationship was looked at in two ways. First, we were concerned with the . potential for shunting under the superior bridging leaflet (none, through interchordal spaces, or under a free leaflet) (Table I). If the superior leaflet was firmly fixed to the septum, so was the inferior leaflet (2/2). If there was the potential for interchordal shunting under the superior leaflet, there was similar potential under the inferior leaflet in 75% of the cases. A free superior leaflet was almost equally associated with a potential
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Fig. I I. The two common patterns of the inferior bridging leaflet found in atrioventricular septal defects with common valve orifice. Both are sectioned in a four-chamber plane. There is a common floating leaflet in (a), while in (bj the leaflet is divided by a raphe along the septum, with chords producing septal tethering. RA, Right atrium. RV, Right ventricle. LA, Left atrium. L V, Left ventricle. A V. Atrioventricular.
Table I. Relationship of inferior to superior bridging leaflet
Table II. Rastelli classification and leaflet morphology
No·~1 No,
No
VSD
I
lnterchordai shunt
I
No VSD
Intcrchordal 2 24 44
2 3 4
Free
18 23
~
7
3 20
Superior bridging leaflet Free
Superior No VSD Interehordal shunt Free leaflet
B-C
3 17
l.egend: YSD. Ycntricular septal defect.
free or interchordal communication under the inferior leaflet. The second way was to divide the group into the Rastelli subtypes and look at the anatomic potential for shunting (Table II). A free communication beneath the superior bridging leaflet was much more common with the types B, B/C, and C. In the types A and B, it was more common to have interchordal rather than free communication under the inferior leaflet. In the B/C and C varieties, it was equally or more likely to have the anatomic potential for free shunting, In only two hearts of the 70 cases that we were able to categorize was the potential for shunting greater under the inferior than the superior leaflet.
No VSD
Interchordal Free
.
2
2
24 44
20 7
I 10
Inferior bridging leaflet 9 5 3 41 20
21 3
7 1
1
4
3
9 13
Legend: YSD. Ycntricular septal defect.
Comparison of atrioventricular septal defects with other hearts. Ratio of the inlet/outlet dimension of the left ventricle. The value of the inlet/outlet dimensions was significantly less in hearts with atrioventricular septal defects than in those with perimembranous ventricular septal defects, isolated mitral "clefts," or structurally normal hearts. There was no significant difference between the values for the groups with separate versus common orifices or between the Rastelli subtypes (Table III). Ratio of the scooped portion/outlet dimension of the left ventricle. There was no significant difference
Volume 90 Number 4 October, t985
Atrioventricular septal defects
Table ID. Inlet/outlet (I/O) left ventricular dimensions Normal hearts Cleft mitral valve Ventricular septal defect Perimemb. inlet Perimemb. outlet/trab, Atrioventricular septal defects* Separate orifices Common orifice A B B-C C
No.
I/O ± SD
10 7
0.99 ± 0.01 0.98 ± 0.03
20 30
0.98 ± 0.02 0.98 ± 0.02
35 85 38 15 9 23
0.76 0.74 0.73 0.75 0.76 0.75
± ± ± ± ±
±
0.07 0.08 0.07 0.09 0.06 0.09
Legend:SD, Standard deviation. "The difference between the values for atrioventricular septal defects and the other hearts is statistically significant (p < 0.001) in each comparison.
between the groups with separate or common orifices or between the Rastelli subtypes (Table IV). Morphology of the left atrioventricular valve. In the 10 normal hearts, the circumferential attachment of the mural leaflet made up 64% of the entire annular circumference of the mitral valve. The measurements for isolated "clefts" and for all hearts with perimembranous ventricular septal defects showed no significant difference to the normal (Table V). In contrast, the attachment of the mural leaflet was significantly smaller for all atrioventricular septal defects (p < 0.001), whichever of the two methods of measurement was used (see Fig. 2). There was no significant difference among the different types of atrioventricular septal defect. Additional malformations in atrioventricular septal defects. Presence of associated defects. Associated defects were present in both separate and common orifice cases (Table VI). Abnormal outflow tract malformations (tetralogy of Fallot and double-outlet right ventricle), total anomalous pulmonary venous connection, and pulmonary atresia were all more frequent in association with common orifice. Left atrioventricular valve abnormalities and hypoplastic left ventricle were more frequent in the group with separate orifices. Coarctation was associated with both groups. Except for the more frequent association of right ventricular outflow tract abnormalities and free-floating leaflets and, in this series, hypoplastic left ventricle with minimal bridging of the superior leaflet, there was no pattern of specific anomalies associated with the Rastelli subtypes. Presence of Down's syndrome. Of the 35 specimens with a separate atrioventricular orifice, only four (11 %) were obtained from patients with Down's syndrome. None of these hearts had any associated defects.
6 19
Table IV. Ratio of scooped portion ventricular
septum/outlet dimension of left ventricle (8/0) S/O
No. Separate orifice Common orifice A B B-C C
0.67 0.59 0.57 0.63 0.59 0.58
35 85 38 15 9 23
± ± ± ± ± ±
0.07* 0.08* 0.08 0.10 0.05 0.08
"The difference is not statistically significant.
Table V. Left atrioventricular valve-eircumferential
attachment of mural leaflet Circumference Normal hearts Isolated cleft Ventricular septal defect Perimemb. inlet 20 30 Preimemb. outler/trab. Atrioventricular septal defects* Separate orifices 35 Common orifice 85 A 38 B 15 B-C 9 C 23
0.64 ± 0.04 0.60 ± 0.03 0.61 ± 0.05 0.62 ± 0.06 Method 1 0.30 ± 0.08 0.31 ± 0.07 0.28 ± 0.07 0.33 ± 0.07 0.34 ± 0.06 0.34 ± 0.07
Method 2 0.17 ± 0.06 0.18 ± 0.05 0.15 ± 0.05 0.20 ± 0.05 0.21 ± 0.05 0.19 ± 0.05
"The difference between the values for atrioventricular septal defects and the other hearts are statistically significant (p < 0.001) whichever method of measurement is considered.
Down's syndrome was more common in the group with a common atrioventricular orifice, 39 of 95 specimens (41%). Again, there was a paucity of associated defects (Table VII). There was no propensity for any of the Rastelli subtypes. Discussion Our further study of hearts with deficient atrioventricular septation has endorsed the measurements performed and the conclusions drawn by Piccoli and associates.?" Indeed, they go further and provide hard scientific evidence to support the contention of Becker and Anderson" that, if the valve leaflets are removed, there is no way of distinguishing the variants of this group from one another. However, while our measurements show conclusively that all lesions with the stigmata of atrioventricular septal defects have a comparable ventricular mass and atrioventricular junction, they also show that other hearts often grouped with these malformations do not share these unifying features. Thus, it is often suggested that hearts with a perimembranous deficiency of the muscular inlet septum, and others with an isolated "cleft" in the anterior (aortic) leaflet of the mitral valve, should be considered as "formes fruste" or
The Journal of
6 20 Penkoske et al.
Thoracic and Cardiovascular Surgery
Table VI. Associated anomalies Common orifice In = 95)
Separate orifices In = 35)
I
No.
10 10 0 3
Hypoplastic left ventricle Coarctation TOF/DORV Double-orifice left A V valve Parachute left AV valve Ebstein's right AV valve Total anomalous pulmonary VC Pulmonary atresia Duct Hypoplastic right ventricle Down's syndrome
29 29 9 II
4 I
3
0 0 4
II
4
II
I.
No.
%
%
10
II
21 19 I
22 20
2 2
2 2
2 5 6 I 39
2 3
I
6 I 41
Rastelli type Anomaly Hypoplastic left ventricle Coarctation TOF/DORV Left AV valve abnormality Pulmonary atresia Right AV valve abnormality TAPVC Hypoplastic right ventricle Duct Down's syndrome
No.
A
10
6
21 19
10 3
3 5
I I
2 2
I
B I I 4 I
I
BIC
I
I 4
3 13
2 8 6 I
2
2
I
I I I
I
6 39
C
8
5
I
Unclassified* I I 2
2
I
8
5
Legend: TOF, Tetralogy of Fallot, DORV, Double-outlet right ventricle. AV, Atrioventricular. VC, Venous connection. 'Usually a postoperative specimen in which this specific feature was unclear.
"incompletely expressed" examples of atrioventricular septal defects (atrioventricular canal malformations, endocardial cushion defects}.14, 15 This is not the case. Hearts in neither of these categories have anything in common with atrioventricular septal defects in terms of their overall anatomy. This is particularly significant in the case of an isolated "cleft" of the mitral valve.15 We will discuss in depth the matter of the left valve in atrioventricular septal defects. Suffice it at this stage to indicate that, very rarely, hearts can exist with all the stigmata of an atrioventricular septal defect, including a trifoliate left valve, but with intact septal structures." If hearts are to be defined as "incompletely expressed" examples of this group, it is the latter anomalies that should be thus considered. Our study has therefore clarified for us with hard measurements the precise nature of what is and what is not an atrioventricular septal defect. It has also enabled us better to appreciate how those lesions in this group with, on the one hand, common orifice and, on the other hand, separate right and left atrioventricular orifices are characterized more by their similarities than by their differences. It is the similarity among the hearts that
defeats attempts to characterize them in terms of "completeness' or "partialness." These subdivisionshave been related more to concepts of embryology than to observations of anatomy. The measurements we have done show that the morphology of the so-called "complete" variant differs from the so-called "partial" variant only in the absence of a connecting tongue of valve tissue between the facing surfaces of the two bridging leaflets. Attempts to classify completeness according to the potential for shunting between the cardiac chambers necessitates the provision of various "intermediate" or "transitional" categories. I, 2, 17 The problem with all these attempts at "pigeon-holing" is that the major variables, namely the state of the atrioventricular orifice and the anatomic potential for shunting through the atrioventricular septal defect, are not mutally dependent. Thus, with a common orifice the anatomic potential for shunting can be confined to the atrial level when the bridging leaflets are firmly adherent to the septum although not joined by a connecting tongue. Similarly, hearts with separate right and left orifices can exist with free-floating leaflets so that there is anatomic potential for considerable shunting at the ventricular level.All this
Volume 90 Number 4 October, 1985
information cannot be conveyed in a single term. Instead, it is preferable to describe separately the state of the atrioventricular junction (common orifice or separate orifices) and the anatomic potential for shunting between the cardiac chambers. The other areas in which attempts have been made to pigeon-hole the anatomy is in the morphology of the bridging leaflets. In this respect, the seminal study of Rastelli, Kirklin, and Titus' represented a major step forward in our knowledge. As stated by Piccoli and colleagues," subsequent studies endorsed the observations of this group' but questioned their interpretation. Our present study confirms this opinion. Furthermore, examination of our hearts shows that the spectrum they described can be expanded to include examples with separate valve orifices. When the Rastelli classification' is interpreted in terms of degree of bridging of the superior leaflet rather than division of a common leaflet, then it can easily and logically be expanded to incorporate those hearts with separate valve orifices (ostium primum atrial septal defect). Rastelli, Kirklin, and Titus' themselves in a footnote (reference 33, p. 308) pointed to the analogy between their type A lesion and the arrangement of the normal tricuspid valve. McGoon, Puga, and Danielson 14 then showed that in most "partial" defects the anterior component of the septal leaflet of the tricuspid valve was deficient. Our study endorses their observation. However, deficiency of the leaflet is caused by the superior bridging leaflet being turned-in to be attached in linear fashion to the right ventricular surface of the septum. Our specimens show the intermediate forms of this spectrum, in which the right ventricular component of the superior leaflet stands free in the presence of separate orifices. Furthermore, in a single specimen we observed increased bridging of the superior leaflet comparable to the Rastelli type B variant but still with separate right and left valve orifices. The only logical interpretation of these findings is that presaged by Studer and co-workers," namely that the spectrum of lesions incorporated within the Rastelli classification be expanded to include cases with separate valve orifices (partial defects or ostium primum atrial septal defect). Having said that, we must then ask if this categorization will be of surgical significance. McGoon, Puga, and Danielson 14 are convinced of its value. Others are less so. I I. 18 There is no doubt concerning its anatomic validity. There are, however, significant differences in the observations obtained at autopsy-" and those at operation. Surprisingly few type B variants are observed by the surgeon. Yet these lesions made up 15% of the original series' and 18% of our hearts. A further 11% of our cases were intermediate between
Atrioventricular septal defects
621
Table VB. Down's syndrome and associated anomalies Down's syndrome Non-Dawn's Defect Hypoplastic left ventricle Coarctation TOF/DORV Double-orifice left A V valve Parachute left A V valve Ebstein's right A V valve Total anomalous pulmonary VC Pulmonary atresia Duct Hypoplastic right ventricle
(n = 39)
(n = 56)
I
9
5
16
2
17
o
2 2 2 5 4 I
o
o o o 2 2
I
For legend see Table VI.
types B anc C. The reason for this was pointed out by Rastelli, Kirklin, and Titus. 3 The anomalous papillary muscle supporting the commissure between the superior bridging and the anterosuperior leaflet is best seen from the infundibular aspect, a view unfortunately denied in most cases to the surgeon. Thus, the important subtlety of the Rastelli classification is rarely of full value in the operating room. The other potential disadvantage of the classification is that it took no cognizance of the inferior bridging leaflet. Rastelli, Kirklin, and Titus' and subsequent investigators have suggested that there is no relationship between the state of the inferior leaflet as compared with the superior one. Our findings would suggest this to be an overstatement. In terms of tethering of the leaflet, the arrangement was the same for both leaflets in a significant number of hearts. This relationship, however, was insufficiently constant to be predictive. Each case must therefore be treated on its own merits and examined carefully to determine the morphology and attachments of both bridging leaflets. We can endorse the statement of Ebert and Goor" that, almost without exception, the greatest potential for shunting is beneath the superior bridging leaflet. The adjudication of the surgical value of these observations requires further studies in the mold of that of Studer and associates," which analyzes the whole spectrum of atrioventricular septal defects. The outstanding question concerning atrioventricular septal defects remains the nature of the left atrioventricular valve. The anatomic nature of this valve has been obscured by two features. First, the categorization of the lesions has been conducted on embryologic rather than anatomic premises. Second, there has been disagreement concerning the role in surgical repair of closure of the so-called "cleft." Both of these matters are extraneous to the anatomic issues. Our present study has shown
. The Journal of
6 2 2 Penkoske et al.
unequivocally that the left valve in atrioventricular septal defects bears resemblance neither to the normal mitral valve nor to the mitral valve with a perimembranous inlet, ventricular septal defect, or with an isolated "cleft." This observation is certainly not original. The potential dangers in closing the so-called "cleft" were discussed by both Frater" and Van Mierop and Alley." At more-or-less the same time, Rastelli, Kirklin, and Titus' commented that "it is concluded that the term is inappropriate." Yet the use of the term persisted, as did the concept of a naturally occurring breach between the components of the anterior leaflet of the mitral valve. It is Carpentier" who deserves the credit for emphasizing that the left valve differs not only in terms of the leaflets but also in terms of papillary muscle disposition, but even he continued to call it a mitral valve. Why should we call it a mitral valve when it has none of the features associated with that structure other than residing within the morphologically left ventricle? The merits of closing or not closing the functional commissure ("cleft") between the left ventricular components of the bridging leaflets remain to be established in a scientific manner. We submit that this will be accomplished only when it is fully appreciated that the left valve in atrioventricular septal defects is a trifoliate structure with scant resemblance to the normal mitral valve. The significance of this single fact is clearly demonstrated in the recent and excellent study of Rizzoli and his colleagues.22
2
3
4
5 6
7
8
REFERENCES Wakai CS, Edwards JE: Developmental and pathologic considerations in persistent common atrioventricular canal. Mayo Clin Proc 31:487-500, 1956 Wakai CS, Edward JE: Pathologic study of persistent common atrioventricular canal. Am Heart J 56:779-794, 1958 Rastelli GC, Kirklin JW, Titus JL: Anatomic observations on complete form of persistent common atrioventricular canal with special reference to atrioventricular valves. Mayo Clin Proc 41:296-308, 1966 Goor D, Lillehei CW, Edwards JE: Further observations on the pathology of the atrioventricular canal malformation. Arch Surg 97:954-962, 1968 Bharati S, Lev M: The spectrum of common atrioventricular orifice (canal). Am Heart J 86:553-561, 1973 Ugarte M, de Salamanca FE, Quero M: Endocardial cushion defects. an anatomical study of 54 specimens. Br Heart J 38:674-682, 1976 Piccoli GP, Gerlis LM, Wilkinson JL, Lozsadi K, Macartney FJ, Anderson RH: Morphology and classification of atrioventricular defects. Br Heart J 42:621-632, 1979 Piccoli GP, Wilkinson JL, Macartney FJ, Gerlis LM,
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10
11
12
13
14
15
16
17
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22
Anderson RH: Morphology and classification of complete atrioventricular defects. Br Heart J 42:633-639, 1979 Becker AE, Anderson RH: Atrioventricular septal defects. What's in a name? J THORAC CARDIOVASC SURG 83:461469, 1982 Carpentier A: Surgical anatomy and management of the mitral component of atrioventricular canal defects, Paediatric Cardiology 1977, RH Anderson, EA Shinebourne, eds., Edinburgh, 1978, Churchill Livingstone, pp 477486. Anderson RH, Zuberbuhler JR, Penkoske PA, Neches WH: Of clefts, commissures, and things. J THORAC CARDIOVASC SURG 90:605-610, 1985 Berger TJ, Kirklin JW, Blackstone EH, Pacifico AD, Kouchoukos NT: Primary repair of complete atrioventricular canal in patients less than 2 years old. Am J Cardiol 41:906-913, 1978 Studer M, Blackstone EH, Kirklin JW, Pacifico AD, Soto B, Chung GKT, Kirklin JK, Bargeron LM: Determinants of early and late results of repair of atrioventricular septal (canal) defects. J THORAC CARDIOVASC SURG 84:523-542, 1982 McGoon DC, Puga FJ, Danielson GK: Atrioventricular canal, Gibbon's Surgery of the Heart, DC Sabiston, FC Spencer, eds., Philadelphia, 1983, W. B. Saunders Company, pp 1051-1066 Di Segni E, Edwards JE: Cleft anterior leaflet of the mitral valve with intact septa. A study of 20 cases. Am J Cardiol 51:919-926, 1983 Silverman NH, Ho SY, Anderson RH, Smith A, Wilkinson JL: Atrioventricular septal defect with intact atrial and ventricular septal structures. Int J Cardiol 5:567-572, 1984 Bharati S, Lev M, McAllister HA, Kirklin JW: Surgical anatomy of the atrioventricular valve in the intermediate type of common atrioventricular orifice. J THORAC CARDIOVASC SURG 79:884-889, 1980 Norwood WI, Castaneda AR: Atrioventricular canal defects. Partial, intermediate and complete, Thoracic and Cardiovascular Surgery, WWL Glenn, ed., Norwalk, Conn., 1983, Appleton-Century-Crofts, pp 757-769 Ebert PA, Goor DA: Complete atrioventricular canal malformations. Further clarification of the anatomy of the common leaflet and its relationship to the VSD in surgical correction. Ann Thorac Surg 25:134-143, 1978 Frater R WM: Persistent common atrioventricular canal. Anatomy and function in relation to surgical repair. Circulation 32: 120-129, 1965 Van Mierop LHS, Alley RD: The management of the cleft mitral valve in endocardial cushion defects. Ann Thorac Surg 2:416-423, 1966 Rizzoli G, Mazzucco A, Brumana T, Valfre C, Rubino M, Rocco F, Daliento L, Frescura C, Gallucci V: Operative risk of correction of atrioventricular septal defects. Br Heart J 52:258-265, 1984